Many tasks previously performed by humans are now accomplished by robotic machines controlled by a stored program of instructions. These tasks include repetitive operations adaptable to machine implementation, operations in hazardous areas or involving handling of hazardous articles, processes accomplished in environments not conducive to human workers and operations requiring precision maneuvering and positioning of work objects. For example, in the semiconductor fabrication field, robots are used in a clean room environment to transport, handle and process semiconductor components including silicon wafers, chips and packaged integrated circuits. Each robotic device interacts with other robotic devices and with human workers stationed in the work space to supervise, control and perform other adjunct processes.
Associated safety systems are used to detect collison hazards and control robot operations accordingly. Collision hazards may be caused by intrusion of a foreign object such as a human, another robotic device, or some other material into a work envelope or work area of the robotic device. Current state of the art multiple beam infrared detection systems, commonly known as "light curtains", are used to prevent robotic systems from coming into contact with obstacles that enter the work envelope. An example is a human entering the work envelope of the X axis of a linear travel-type robot system.
As shown in FIG. 1, a multiple beam infrared detection system includes an infrared transmitter unit 22 including an infrared emitter module 24. Emitter module 24 includes a plurality of vertically aligned infrared light emitting diodes for emitting a plurality of parallel infrared light beams 26 forming a "light curtain" 28 between transmitter assembly 22 and opposing infrared receiver assembly 30. Light curtain 28 defines a vertically oriented planar area along one side or wall of the work envelope. The infrared light beams are received by infrared receiver unit 30 which includes an infrared detector assembly 32 for detecting infrared light beams 26. Assembly 30 comprises a plurality of vertically aligned infrared detectors such as phototransistors or photodiodes for receiving and detecting respective light beams 26. Associated control electronics process signals from detector assembly 32 to supply a logic signal. The logic signal provides an indication of an interruption of any of the light beams 26 forming curtain 28.
A machine such as a linear travel-type robot system 40 is located behind light curtain 28 within the work envelope. Robot 40 is maneuverable along the X axis on platform 42 in response to control signals supplied by a robot controller. The light curtain is used to prevent the robotic system from maneuvering into contact with obstacles that enter the work envelope by inhibiting robot motion upon detection of an object penetrating the light curtain. When interrupted, the light curtain system actives a complete safety stop of the X axis motion of the robot to avoid a collison with the obstacle. A light curtain system similar to that described is disclosed in Blau, U.S. Pat. No. 5,015,840, incorporated herein by reference and is commercially available from manufacturers including Triad Controls, Inc. of Pittsburgh, Pa., and Scientific Technologies Inc. of Hayward, Calif.
In another configuration, a multi-sided guarding system includes a plurality of mirrors for reflecting infrared light beams to enclose a work envelope. A wrap-around light curtain is also used to provide a multi-sided guard for moving equipment, robots or machinery to prevent injury to personnel and to prevent damage to equipment when maneuvered in the presence of a foreign object in the work envelope. Referring to FIG. 2, infrared transmitter assembly 22 emits a plurality of vertically spaced parallel light beams 26 using an array of light emitting diodes to form a light curtain 28. Corner mirrors 34 reflect the light beams to infrared receiver unit 30 positioned immediately adjacent infrared transmitter unit 22 to enclose the work envelope within the light curtain. A machine such as a pick-and-place robot 44 is located within the work space and is responsive to a stored program for performing nominal maneuvering operations and to interruption of the light beams to halt all movements. Penetration of the light curtain halts robotic motion to prevent injury to personnel and avoid damage to the robotic apparatus by a foreign object.
As described, detection of a foreign object penetrating a light curtain completely inhibits or disables motion of a robotic device to avoid injury to personnel and damage to the device. However, light curtain systems operate to disable robotic operations regardless of the distance between the obstacle and the position of the robot. If a light beam forming the curtain is broken, a full electromechanical stop of the robotic device is initiated. This can result in over-protection of the robot operating envelope. For example, in the long length linear motion system shown in FIG. 1, the obstacle may actually not pose any hazard to operation, particularly if the distance between the current position of the robot and the obstacle is beyond the true requirements for safe operation. Similarly, in the wrap-around system depicted in FIG. 2, pick-and-place robot 44 may be positioned and maneuvering in a portion of the work envelope which would not create a hazard to personnel entering a far side of the envelope.
Accordingly, a need exists for a safety interlock system for detecting entry of a foreign object into a work envelope and selectively inhibiting mechanical operations of a machine in response to proximity of the object to the machine.
A need further exists for a safety interlock system for progressively inhibiting mechanical operations of a machine in response to a decreasing distance between the machine and a detected obstacle.
A need further exists for selectively decreasing a maneuvering speed of a robotic device in response to detection of an obstacle approaching the robotic device.
A need further exists for a safety interlock system including a fail-safe operation which inhibits operations of a mechanical device located in a work envelope upon detection of a foreign obstacle entering the work envelope when a distance between the machine and foreign object cannot be determined.
A need further exists for a method of maneuvering an apparatus within a work envelope which is responsive to penetration of a foreign object into the work envelope and a distance between the apparatus and the foreign object.